Scissors lift with height sensor system

ABSTRACT

A scissor lift with a height sensor system includes a scissors assembly including at least one scissor leg configured to lower and raise a platform, an angle sensor configured to sense the angular position of a pivot pin about which the scissor leg pivots, and a processor configured to calculate a height of the platform from the angular position sensed by the angle sensor. The processor may also be configured to control the lift actuator in response to the height of the platform calculated from the angular position sensed by the angular sensor. The angle sensor may be a magnetic angle sensor configured to sense the angle of a magnetic angular marker attached to the pivot pin.

RELATED APPLICATION

This is a Continuation of U.S. application Ser. No. 15/337,018, filed onOct. 28, 2016. The entire contents of this application are expresslyincorporated herein by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to a scissors lift, and moreparticularly, to a scissors lift with a height sensor system.

BACKGROUND

Lifts are used in a variety of different applications to raise and lowerobjects and/or people from a first elevation to at least a secondelevation. In an industrial setting (e.g., a factory or warehouse), alift may be used to transport heavy machinery and pallets of goods toand from balconies, mezzanines, basements, and/or between floors. Threetypes of lifts commonly used in an industrial setting are verticalreciprocating conveyors (VRCs), elevators, and scissor lifts.

A VRC typically includes a platform that supports the cargo and a pairof spaced apart vertical guide columns which guide the platform along avertical path between the lower and upper levels. Fewer or more verticalguide columns may be utilized by the VRC (e.g., three or four verticalguide columns) depending on the application and type of cargo. Some VRCsemploy a single mast from which the platform is cantilevered. To changethe height of the platform, most VRCs employ an automated pulley that ismounted on a crossbar spanning the vertical guide columns and connectedto the platform via a belt or chain. In general, safety regulationslimit VRCs to carrying cargo and not passengers.

An elevator generally includes an enclosed car having a retractabledoor, a counterweight, a hoistway or shaft through which the cartravels, a drive system, and various safety features that prevent freefall such as brakes and a governor. The safety features and design of anelevator make it suitable for human passengers, but the costs ofinstalling and maintaining the elevator as well as other functionallimitations may outweigh the benefit of human passengers in someindustrial applications.

Scissor lifts employ a plurality of linked, folding supports arranged ina generally crisscross pattern that form one or more pantographassemblies to operatively connect the platform to a base. The platformis raised by applying pressure to at least one of the folding supportsin a manner that elongates the crisscross pattern and thereby propelsthe platform vertically. Descent is accomplished by collapsing thecrisscross pattern. The crisscross pattern of folding supports is fairlyresistant to sway and thus results in a relatively stable platform. Assuch, regulations typically allow an operator of a scissor lift to rideon the platform together with the cargo.

One common way to power a scissor lift is to provide a hydraulicactuator that exerts pressure on one of the folding supports to move thefolding support into an upright position. The other folding supports, byvirtue of their linked connection to the actuated folding support, arealso moved upright, thereby causing the entire crisscross pattern offolding supports to elongate and push the platform in the upwarddirection.

It is desirable to be able to calculate the height of the platformwithout necessarily directly measuring the height of the platformitself. This can be useful for controlling the scissor lift to positionthe platform at a desired height.

SUMMARY

According to some aspects of the disclosure, a scissors lift with aheight sensor system includes a scissors assembly including at least onescissor leg configured to lower and raise a platform, an angle sensorconfigured to sense the angular position of a pivot pin about which thescissor leg pivots, and a processor configured to calculate a height ofthe platform from the angular position sensed by the angle sensor.

In one exemplary arrangement, a scissors lift with a height sensorsystem includes a base, a platform, a scissors assembly, a liftactuator, an angle sensor, and a processor. The platform is movablebetween a first height and a second height. The scissors assemblyincludes at least one pivotally connected scissor leg and operativelyconnects the base with the platform. The scissors assembly is configuredto lower and raise the platform relative to the base. The lift actuatoris configured to pivot, either directly or indirectly, the scissor legabout a pivot pin to selectively raise and lower the platform. The anglesensor is configured to sense the angular position of the pivot pin. Theprocessor is configured to calculate a height of the platform from theangular position sensed by the angle sensor. Optionally, the processormay also be configured to control the lift actuator in response to theheight of the platform calculated from the angular position sensed bythe angular sensor.

In some arrangements, the pivot pin may be secured to the scissor leg torotate with the scissor leg, and the angle sensor may be held in a fixedposition adjacent the pivot pin. In other arrangements, the angle sensormay be secured to the scissor leg to rotate with the scissor leg, andthe pivot pin may be held in a fixed position adjacent the pivot pin.

In some arrangements, an angle position marker may be disposed at adistal end of the pivot pin. The angle sensor may be disposedimmediately opposite and facing the angle position marker. The anglesensor may sense the angular position of the angle position marker. Theangle sensor may include a magnetic sensor that senses the angularposition of a magnet. The angle position marker may include a magnetthat uniquely identifies the angular rotation of the pivot pin. Themagnet may be a permanent magnet or another type of magnet. The magneticsensor may include a Hall effect sensor. In some arrangements, the anglesensor may include an optical sensor that optically senses the angularposition of the angle position marker.

In some arrangements, the scissors lift may include a clevis thatcouples the scissor leg to the base. The pivot pin may extend from thescissor leg through a bore in the clevis. The angle sensor may beattached to the clevis. The clevis may include a first support flangespaced apart from a second support flange with a gap defined between thefirst and second support flanges. The angle sensor may be attached tothe first support flange, and the pivot pin may extend through thesecond support flange. The angle sensor may face the distal end of thepivot pin across the gap. The angle sensor may be axially aligned withthe longitudinal axis of the pivot pin.

In some arrangements, the pivot pin is part of a pin assembly includinga pin flange, a bearing shaft extending from the pin flange, and anangle position marker readable by the angular sensor and disposed at adistal end of the bearing shaft. The pin flange may be secured to thescissor leg. The bearing shaft may rotate with and support the scissorleg, and the angle position marker may rotate with the bearing shaft.The angle position marker may be carried by a retainer plug fixed in thedistal end of the bearing shaft. The bearing shaft and/or the retainerplug may be made of non-ferrous materials.

In some arrangements, the scissors lift may include an operator controlinterface operatively connected to the processor to provide inputcommands to the processor for controlling the height of the platform.

In some arrangements, the scissors assembly may include at least onepair of scissor legs pivotably connected in the form of an X, whereinthe scissor leg is one of the pair of scissor legs. In otherarrangements, the scissors assembly may include at least two such pairsof scissor legs aligned in parallel with each other, for example,supporting opposite sides of the platform. One or more additional suchpairs of scissor legs may be connected in series to the end of one orboth of the first and second pairs of scissor legs. Other arrangementsof scissor legs configured to support, raise, and lower the platform arealso possible.

These and additional aspects of the disclosure, arrangements, and/orfeatures will become apparent upon studying the following detaileddescription of an exemplary arrangement and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a scissors lift according to one aspectof the disclosure in a fully raised position;

FIG. 2 is an end view of the scissors lift in a fully lowered position;

FIG. 3 is an enlarged view of the sensor assembly installed on thescissors lift in the circled portion A of FIG. 1;

FIG. 4 is an enlarged detail view of the sensor assembly in the circledportion B of FIG. 2;

FIG. 5 is an enlarged isometric view of a pin assembly of the anglesensor in isolation;

FIG. 6 is a cross-sectional view of the pin assembly of FIG. 5 along thelongitudinal axis of the pin; and

FIG. 7 is an electrical schematic diagram of a processor and relatedcircuitry for calculating the height of the platform based on readingsfrom the sensor assembly and/or controlling the height of the platform.

DETAILED DESCRIPTION

In some aspects, a scissors lift is provided a height sensor and/orcontrol system that includes a magnetic angle sensor that senses theangular position of a pivot pin of one of the scissor legs and convertsthat angle measurement into a height measurement of a platform at thetop of the scissors lift. The pivot pin may be any one of the pivot pinsthat rotates correspondingly with angular rotation of the scissor leg asthe scissor legs extend and retract to move the platform up and/or down.In one arrangement, the pivot pin connects one of the bottom scissorlegs with the base of the scissors lift. However, the magnetic anglesensor may be configured to sense the angular position of other ones ofthe pivot pins as long as the pivot pin and the angular sensor arearranged to sense the angular movement of either the pin or the angularsensor that directly correlates to angular movement of the scissor legor legs.

In some arrangements, a magnetic marker is attached to the end of thepivot pin and rotates with the pivot pin. The magnetic angle sensor ispositioned adjacent to the magnetic marker and held in position by abracket. The magnetic angle sensor includes a Hall effect type magneticsensor that senses the angular position of the magnetic marker (and thusalso of the pivot pin).

Readings from the magnetic angle sensor are provided to a processor,which is programmed to convert the angular readings into an absoluteheight of the scissors lift through mathematical calculations. Theheight calculations can be used for controlling the height of thescissors lift. For example, the height calculation may be used by aprocessor to send control instructions to a lift drive to move the liftup and/or down to a desired height.

Other types of angle sensors may be used, and other physicalarrangements of the angle sensor relative to the pivot pin are alsopossible, as discussed in further detail herein.

Turning now to the exemplary arrangement of the drawings, FIGS. 1-6illustrate one exemplary embodiment of a scissors lift 10 having aheight sensor and/or control system according to the present disclosure.The scissors lift 10 includes a platform 12, a base 14, and a scissorsassembly 16 that moves the platform 12 up and down relative to the base14. The scissors assembly 16 is configured to move the platform 12between a fully lowered position (i.e., fully retracted scissorsassembly) as shown in FIG. 5 and any one or more intermediate raisedpositions to a fully raised position (i.e., fully extended scissorsassembly) as shown in FIG. 1. The height sensor and/or control system isconfigured to calculate the height of the platform 12 relative to thebase 14. Optionally, the height sensor and/or control system ispreferably also configured to use the calculated height of the platform12 to control movement of the scissors assembly 16 and thereby controlthe height of the platform 12.

The base 14 may take any form suitable for operably supporting thescissors assembly 16 so that the scissors assembly 16 can extend andretract. In this example, the base 14 is in the form of a rectangularframe 18 that forms two parallel tracks 20 that support the scissorsassembly 16. The rectangular frame 18 may be formed for example of steelangle sections or other materials or other shaped members. The tracks 20may simply be formed by the flanges of the angle sections. However, anyother form of the frame 18 suitable for operably supporting the scissorsassembly 16 and forming the tracks 20 may be used. Similarly, theplatform 12 may take any form suitable for being operably supported bythe scissors assembly 16 to be able to raise and lower the platform 12.In this example, the platform 12 includes a deck suitable for supportinga load that rests upon the top end of the scissors assembly 16 andincludes appropriate tracks similar to the tracks 20 to allow thescissors assembly 16 to extend and retract. However, other forms of theplatform 12 may be used.

The scissors assembly 16 is formed by a plurality of pivotally connectedscissor legs 22 arranged in a crisscross pattern that form one or morepantograph assemblies, and one or more lift actuators 24 configured toextend and retract the scissors assembly 16. In this example, thescissors assembly 16 includes two parallel pairs of pivotably connectedscissor legs 22 a and 22 b, a left pair and a right pair, each pair ofscissor legs 22 a/b pivotally connected with each other by a centralpivot pin 22 c through a middle portion of the legs. Thus, each pairscissor legs 22 a/b forms an X such that the pair of scissor legs 22/bcan pivot about the pivot pin. The left pair of scissor legs 22 a/b isconnected to the right pair of scissor legs 22 a/b by one or more crossmembers 26 such that the left pair of scissor legs and the right pair ofscissor legs extend and retract in tandem. The lift actuators 24 in thisexample include a pair of hydraulic cylinders, each cylinder having oneend operably coupled to a cross member 26 between one parallel set ofscissor legs 22 and the opposite and operably coupled to a cross member26 between the other parallel set of scissor legs 22 such that extendingor retracting the hydraulic cylinders causes the scissor legs 22 torotate about the central pivot pin 22 c and thereby extend or retractthe scissors assembly 16 accordingly. However, any other type of liftactuator 24 capable of pivoting the pairs of scissor legs 22 a/b may beused. Furthermore, although the present example includes two pairs ofscissor legs 22, additional pairs of scissor legs, either parallel to orin a series extension to the illustrated scissor legs could be used, andthe disclosure is not limited to any one particular scissors assemblyarrangement. Rather, the height sensor and/or control system of thepresent disclosure may be implemented with virtually any type ofscissors lift arrangement.

The height sensor and/or control system includes a sensor assembly 30(FIGS. 3-6) configured to sense rotational movement and/or position ofone or more of the scissor legs 22 via the angular position of a pivotpin and a processor 32 (FIG. 7) configured to calculate the height ofthe platform 12 based on the sensor readings received from the sensorassembly 30, and optionally to also provide control instructions for thelift actuators 24 based on the calculated height. In the exemplaryarrangement, the sensor assembly 30 is configured to sense angularrotational movement of a pivot pin 34 that pivotably connects a firstone of the scissor legs 22 b to the base 14. As the lift actuators 24extend or retract the scissors assembly 16, the scissor leg 22 b rotatesabout the longitudinal axis X of pivot pin 34. The pivot pin 34 isrotationally fixed to the scissor leg 22 b and thereby configured torotate about its longitudinal axis simultaneously and in directcorrelation with the rotation of the scissor leg 22 b. As the pivot pin34 rotates with the scissor leg 22 b, the angle sensor 36 senses theangular position of the pivot pin 34 about its axis. In otherarrangements, the angle sensor 36 could be configured to rotate indirect correlation to the pivoting of the scissor leg 22 b and arotational or angle position marker to be read by the angle sensor 36could be held in a fixed position. In either arrangement, the anglesensor 36 senses the angular position of the pivot pin 34, and bycorrelation, the angular position of the scissor leg 22 b. The sensedrotational position of the pivot pin 34 relative to the angle sensor 36is provided to the processor 32, which is configured to convert theangular position to a calculated height reading of the platform 12 byany suitable calculation method.

As best seen in FIGS. 3-6, the bottom end of the scissor leg 22 b isrotationally coupled to the base 14 by a clevis 38 and the pivot pin 34.The clevis 38 is fixed to the base 14 and includes a pair of supportflanges 40 and 42 extending upwardly from a base portion. The supportflanges 40 and 42 are spaced apart from each other and separated by agap 44. The scissor leg 22 b is pivotably coupled to the support flange42 by the pivot pin 34. In particular, the pivot pin 34 is rotationallyfixed to and extends laterally inwardly from the lateral inner surfaceof the scissor leg 22 b and is journaled within a through bore 46extending laterally through the support flanges 42. The distal end 35 ofthe pivot pin 34 extends into the gap 44, but preferably does not extendacross the entire width of the gap 44, as best seen in FIG. 4. The anglesensor 36 is carried by the support flange 40 axially aligned with andalong the axis X and immediately adjacent the distal end of the pivotpin 34. In this arrangement, the angle sensor 36 is disposed through asecond bore 48 through the support flange 40, wherein the bore 48 isaxially aligned with the bore 46. The angle sensor 36 is fixed inposition in the support flange 40 such that it does not rotate or moveaxially relative to the support flange 40 or the pivot pin 34.Preferably, the angle sensor 36 is fixed in the bore 48 of the supportflange 40, such as by lock nuts, jam nuts, or other fasteningmechanisms, such that the sensing end 39 of the angle sensor is disposedwithin the gap 44 axially aligned with and spaced a small distance apartfrom the distal end of the pivot pin 34, for example less than about 2cm apart, preferably less than about 10 mm apart, and more preferablybetween about 3 mm and 1 mm apart. Thus, as the pivot pin 34 rotatesangularly about its longitudinal axis X, the angle sensor 36 remainsfixed and can sense the angular position and/or change an angularposition of the pivot pin 34.

In this exemplary arrangement, the angle sensor 36 is a magnetic sensorthat can sense changes in a magnetic field in its area. As best seen inFIGS. 5 and 6, in this particular example, the pivot pin 34 is part of apin assembly 50 that includes a pin flange 52, a bearing shaft 54, and arotational or angle position marker 56 that is operatively readable bythe angle sensor. In this arrangement, the angle sensor 36 is a magneticsensor and the angle position marker 56 is a permanent magnet or othertype of suitable magnet; however, other types of angular sensing systemsmay be used. The pin flange 52 is formed of a flat elongate member, suchas a piece of flat steel or iron, and has an eyehole 53 through one endof the elongate member and the bearing shaft 54 extending laterally fromthe other end of the elongate member. In this arrangement, the bearingshaft 54 forms the pivot pin 34, and is preferably formed of chromeplated steel to improve the friction and bearing characteristics,although other materials may also be suitable. The angle position marker56 is fixed into the distal end 35 of the bearing shaft 54 so as torotate with the bearing shaft 54 by any suitable method. In thisarrangement, as best seen in FIG. 6, the angle position marker 56 iscarried by a retainer plug 58, which is preferably threaded to threadinto a threaded bore 60 extending axially into the distal end 35 of thebearing shaft 54. The angle position marker 56 is disposed at the distalend of the retainer plug 58. In this arrangement, the angle positionmarker 56 is a permanent magnet fixed within a cavity 62 having the formof a slotted recess in the distal end of the retainer plug 58. As bestseen in FIG. 5, the angle position marker 56 permanent magnet ispreferably disposed with its north-south magnetic axis aligned along adiameter of the bearing shaft 54 and/or the retainer plug 58 in order toprovide an easily readable angular magnetic signature that can be readby the angle sensor 36. In this arrangement, the permanent magnet 56 isdisposed with its north-south axis aligned generally parallel to theleft end of the pin flange 52. However, the permanent magnet may beaffixed to the distal end of the bearing shaft 54 in other orientationsand by any suitable fixation method. The retainer plug 58 is preferablyformed of aluminum or some other non-magnetic, non-ferrous material.This way, the permanent magnet is the only, or at least the strongest,magnetic field in the region around the distal end 35 of the pivot pin34 within the gap 44 so as to provide accurate magnetic readings by theangle sensor 36. In other arrangements, a non-permanent magnet, such asan electro magnet, could be used in place of or in addition to thepermanent magnet.

As best seen in FIGS. 3 and 4, the pin assembly 50 is attached to thescissor leg 22 b with the bearing shaft 54 extending through a bore 64through the lower end of the scissor leg 22 b and the bore 46 of thesupport flange 42, and with the pin flange 52 secured to the laterallyexterior side of the scissor leg 22 b. A fastener 66, such as a bolt orscrew, is disposed through the eyehole 53 and fixed to the supportflange 42. The bearing shaft 54 is rotationally fixed to the pin flange52 in any suitable manner such that, as the pin flange 52 rotatesangularly with the scissor leg 22 b, the bearing shaft 54 also rotateswithin the bore 46 of the support flange 42. In this manner, the angleposition marker 56 rotates angularly in direct relation to the rotationof the scissor leg 22 b as the scissors assembly 16 extends andcontracts to raise and lower the platform 12. The angle sensor 36includes a Hall effect type magnetic sensor that senses the angularposition of the permanent magnet of the angle position marker 56.Therefore, the readings of the angle sensor 36 from the permanent magnetcan be directly correlated through any of various mathematical formulaeto the height of the platform 12. The angle sensor 36 is operativelycoupled to the processor 32, for example with a wired or a wireless dataconnection, so as to provide the readings of the angle sensor 36 to theprocessor for use in calculating the height of the platform 12.

In another arrangement, the angle sensor 36 could be fixedly attached tothe end of the pivot pin 34 to pivot with the scissor leg 22 b and thepermanent magnet 56 could be fixedly attached to the clevis 38, such asby being affixed in the bore 48 of the support flange 40. In thisarrangement, the angle sensor 36 would rotate axially and the permanentmagnet 56 would remained fixed. The angle sensor 36 still reads theangular position of the angle position marker 56 relative to the anglesensor, and provides the angle readings to the processor 32 for use incalculating the height of the platform 12.

Furthermore, the angle sensor 36 does not necessarily have to be amagnetic sensor, but could be or include another type of angular sensor,such as an optical sensor. In this case, the permanent magnet of theangle position marker 56 could be replaced with or supplemented byanother type of optical rotational or angle position marker capable ofindicating the angular rotational position of the pivot pin 34, such asan optical marker

Turning now to FIG. 7, the sensing and control circuitry of the heightsensor and/or system includes the angle sensor 36, the processor 32, anoperator control interface 70, and a main power supply circuit 72. Theangle sensor 36 is operatively coupled to the processor 32 so as toprovide the sensor reading data, i.e., the sensed angle readings, fromthe angle sensor 36 to the processor 32. The operator control interface70 is also operatively coupled to the processor 32 so that commands canbe provided from the operator control interface 70 to the processor 32to control the height of the platform 12. In this arrangement, theoperator control interface 70 is in the form of a pushbutton control.However, the operator control interface 70 could take on any suitableoperator control interface, such as a touchscreen, a general-purposecomputer, or any other suitable human/machine interface for controllingthe processor 32. The main power supply circuit 72 includes atransformer 76 and other related circuitry configured to provide asuitable supply power to the processor 32, the angle sensor 36, theoperator control interface 70, and optionally any other electricallypowered components on the scissors lift 10, such as a solenoid 78 forcontrolling the lift actuators 24.

The processor 32 in this arrangement includes a central processing unit80, such as a programmable logic circuits (PLC). The central processingunit 80 includes instructions and circuitry configured to convert theangle readings received from the angle sensor 36 into the correspondingheight of the platform 12. This conversion can be calculated in any ofmany different ways. Additionally or alternatively, the PLC can beprogrammed or taught to correlate one or more angle sensor readingsdirectly to corresponding specific heights of the platform 12, up to thegranularity of data produced by the sensor and depending on the capacityand capability of the PLC and the arrangement of the overall controlcircuits. Regardless, because the angular position of the angle positionmarker 56 is directly correlated to the height of the platform 12, theprocessor 32 can continuously or intermittently calculate the height ofthe platform 12 directly from the angle readings received from the anglesensor 36. The calculated height of the platform 12 may be provided to auser, for example by being displayed on a screen or in some other manneruseful to the user.

Additionally or alternatively, the calculated height of the platform 12may be used by the processor 32 to control the up and/or down movementof the platform 12. For example, the processor 32 may use the calculatedheight of the platform to generate appropriate up and/or down drivesignals for the lift actuators 24 to extend and/or retract the scissorsassembly 16 so as to raise and/or lower the platform 12 to a particularselected target height entered by a user. The circuitry for providingthe height control of the platform 12 may take any of many differentsuitable forms and/or implement any suitable algorithm.

To operably install the angle sensor 36 on the scissors lift 10, theplatform 12 is raised to the fully raised position. The angle sensor 36is installed into the clevis 38. Next, the angle sensor 36 is calibratedwith the PLC program. In one possible method, a digital multimeter (DMM)is used to measure the output from the angle sensor 36 after beinginstalled with the platform 12 in the fully raised position. The anglesensor 36 is rotated within the clevis until the DMM reads apre-selected calibration reading. For example, with the circuit of FIG.7, the angle sensor 36 may be rotated such that the DMM readsapproximately 8.5 VDC. With the angle sensor 36 rotated such that itprovides the pre-selected calibration reading, the angle sensor 36 issecured in the clevis 38 so as to be rotationally fixed in the clevis38, and in particular about its longitudinal axis and the longitudinalaxis X of the pivot pin 34, for example, with lock nuts or otherfastening mechanism. With the platform 12 in the fully raised positionand the angle sensor 36 so secured, the angle sensor 36 and theprocessor 32 are calibrated for the fully raised position in anysuitable manner to calibrate the angle sensor's sensor output in thefully raised position to the PLC program. Thereafter, the platform 12 islowered to the fully lowered position, and the angle sensor 36 and theprocessor 32 are calibrated for the fully lowered position in anysuitable manner to calibrate the angle sensor's sensor output in thefully lowered position to the PLC program. Optionally, the steps forcalibrating the angle sensor's output in each of the fully raisedposition and the fully lowered position may be repeated one or moretimes, which may improve the calibration accuracy. Any other suitablemethods for calibrating the angle sensor 36 with the PLC program may beused. After performing the calibration, the scissors lift 10 is readyfor use.

Optionally, the scissors lift 10 may also be calibrated for apre-selected “home” position. To perform the home position calibrationwith the circuit of FIG. 7, the loose wire 82 is attached to the openterminal at TB-2, which allows the up and down pushbuttons 84, 86 to actas constant pressure controls stopping operation when released. The upand down pushbuttons are used to position the platform 12 at a selectedhome position. For example, the initial setting for the home positionmay be approximately in the mid-point of travel between the fully raisedposition and the fully lowered position. However, other positions may beused as a home position. With the platform positioned at the appropriateheight at the home position, the “home” pushbutton 88 is momentarilydepressed, which calibrates the position output from the angle sensor 36to the PLC program. Thereafter, the wires are again disconnected. Anyother suitable methods for calibrating the angle sensor with the PLCprogram may be used.

The scissors lift 10 with a height sensor and/or control system asdescribed herein provides a relatively simple and inexpensive system forcalculating the height of the platform 12 relative to the base 14, andoptionally using that calculated height to provide control of thescissors assembly 16 to move the platform 12 into a desired heightposition.

While the present disclosure has been described with respect to certainembodiments, it will be understood that variations may be made theretothat are still within the scope of the appended claims.

What is claimed is:
 1. A scissors lift with a height sensor system,comprising: a base; a platform movable between a first height and asecond height; a scissors assembly that includes a scissor leg andoperatively connects the base with the platform; a lift actuatorconfigured to pivot the scissor leg about a pivot pin to selectivelyraise and lower the platform; an angle sensor carried by the base andconfigured to rotate with the pivot pin and to sense an angular positionof an angle position marker; and a processor configured to calculate aheight of the platform from the angular position sensed by the anglesensor.
 2. The scissors lift of claim 1, wherein the base comprises aclevis that couples the scissor leg to the base, and wherein the pivotpin extends from the scissor leg through a bore in the clevis, and theangle position marker is attached to the clevis.
 3. The scissors lift ofclaim 2, wherein the clevis includes a first support flange spaced apartfrom a second support flange, and wherein the angle position marker isattached to the first support flange and the pivot pin extends throughthe second support flange.
 4. The scissors lift of claim 1, furthercomprising a pin flange coupled to the pivot pin and defining anaperture, a fastener extending through the aperture to couple the pinflange to the scissor leg.
 5. The scissors lift of claim 1, furthercomprising a pin flange coupled to the pivot pin, the angle sensor beingdisposed at a distal end of the pivot pin, the pin flange being securedto the scissor leg, the pivot pin rotates with and supports the scissorleg.
 6. The scissors lift of claim 1, wherein the base comprises aflange through which the pivot pin extends.
 7. The scissors lift ofclaim 1, wherein the angle sensor is coupled to the pivot pin.
 8. Ascissors lift with a height sensor system, comprising: a base; aplatform movable between a first height and a second height; a scissorsassembly including a scissor leg having a first portion and a secondportion, the first portion of the scissor leg coupled to the platform,the second portion of the scissor leg coupled to the base; a pivot pinextending through the base and the second portion of the scissor leg; anangle sensor carried by the base and configured to sense an angularposition of an angle position marker associated with the pivot pin; anda processor configured to calculate a height of the platform from theangular position sensed by the angle sensor.
 9. The scissors lift ofclaim 8, wherein the base comprises a clevis having flanges that couplesthe scissor leg to the base, and wherein the pivot pin extends through abore in one of the flanges, the angle position marker rotates with thepivot pin, and the angle sensor is coupled to the other of the flanges.10. The scissors lift of claim 8, wherein the base comprises a clevishaving flanges that couples the scissor leg to the base, and wherein thepivot pin extends through a bore in one of the flanges, the angle sensorrotates with the pivot pin, and the angle position marker is coupled tothe other of the flanges.
 11. The scissors lift of claim 8, wherein thepivot pin is secured to the scissor leg to rotate with the scissor leg,and the angle sensor is held in a fixed position adjacent the pivot pin.12. The scissors lift of claim 8, wherein the angle position marker iscoupled to a distal end of the pivot pin.
 13. The scissors lift of claim8, wherein the pivot pin includes a bore that receives the angleposition marker.
 14. The scissors lift of claim 13, further comprising aretainer plug that carries the angle position marker, the retainer plugbeing threadable received in the bore.
 15. A method of operating ascissors lift with a height sensor system, the method comprising:pivoting a scissor leg of a scissor assembly about a pivot pin toselectively raise and lower a platform of a scissors lift relative to abase of the scissors lift, the pivot pin extending through the scissorleg and the base to pivotably couple the scissor leg and the base;sensing, using an angle sensor, an angular position of an angle positionmarker associated with the pivot pin, the angle sensor carried by thebase; and calculating, using a processor, a height of the platform fromthe angular position sensed by the angle sensor.
 16. The method of claim15, wherein the pivoting of the scissor leg about the pivot pin includespivoting the scissor leg relative to a flange through which the pivotpin extends and the sensing of the position of the angle position markerincludes sensing the position of the angle position marker fixed to thepivot pin.
 17. The method of claim 16, wherein the sensing of theposition of the angle position marker includes sensing using the anglesensor fixed relative to the flange.
 18. The method of claim 15, whereinthe sensing of the position of the angle position marker includessensing using the angle sensor fixed relative to the base.
 19. Themethod of claim 15, wherein the pivoting of the scissor leg about thepivot pin includes pivoting the scissor leg relative to a flange throughwhich the pivot pin extends and the sensing of the position of the angleposition marker includes sensing the position of the marker fixedrelative to the flange.
 20. The method of claim 15, wherein the sensingof the position of the angle position marker includes sensing using theangle sensor relative to the pivot pin.